Anus, disorders of

Most anal disorders affect adults and are minor, but they may cause discomfort. Rarely, the anus may fail to develop normally and surgical treatment is needed (see anus, imperforate). In anal stenosis, the anus is too narrow to allow the passage of faeces. Anal fissures originate from tears in the lining of the anus, usually as a result of straining to pass faeces. Cancer of the skin around the anus is rare (see anus, cancer of). Haemorrhoids are enlarged blood vessels under the anal lining. An anal fistula is an abnormal channel connecting the anal canal with the skin surrounding the anus. Itching of the anus is common and may be due to haemorrhoids or other disorders such as threadworm infestation.